Opacifier for vitreous enamels



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COATING OR PLASTIC. 3 1 2 May 7, 1940- w. J. HARSHAW El AL OPACIFIER FORVITREOUS ENAMELS Filed Sept. 15, 1938 3 Sheets-Sheet 1 Fir/n9 Time(Hours) Nut? uuls o\ 2' HWHT? wotU uu U ok /7 77h Oxide 3 5 7 7 Par+s lluorspar Per /00 Par-f5 Compound S25E51 w 0k MH/ add/+10?! WJI-(ggINVENTOR. w, D, 5f/'//wc// BY' MMZZJM. #fln ATTORNEY.

Patented May 7, 1940 I PATENT OFFICE OPACIFIER FOR VITBEOUS ENAMELSWilliam J. Harshaw, Shaker Heights, and William D. Stiliwell, SouthEuclid, Ohio, assignors to The Harshaw Chemical Company, Elyria, Ohio,

a corporation of Ohio Application September 15, 1938, Serial No. 230,104

15 claims.

This invention relates to mill addition opaciflers for vitreous enamels.

Opaciflcation of vitreous enamels is accomplished either by smelteradditions in the production of an enamel frit or by mill additions tothe quenched frit in the production of the enamel slip. Smelter additionopaciflers are often not suitable for mill addition opaciflcation andvice versa.

In our prior United States patent, No. 2,033,707, we have describedpre-calcined mill addition opacifierscapable of imparting to vitreousenamels a high degree of opaciflcation. In enamels wherein we have usedopaciflers according to our said patent, we havev experienced,especially in the case of titanium containing compositions and to someextent also in zirconium containing compositions, a deficiency ofreflectance in the violet. In the case of titanium compositions thisdeflciency appeared as a distinctly perceptible yellowish coloration inthe enamel. Accordingly, it is highly desirable to overcome theindicated tendency to yellow coloration in the enamel by increasing itspower of reflectance of violet light.

In accordance with the present invention it now becomes possible toovercome the undesirable tendency to yellow coloration and produceopacifiers similar to those of our said patent but productive of enamelsexhibiting desirable high reflectance in the violet end of the visiblespectrum.

In the drawings, Fig. 1 is a graphic representation of the efiect ofcalcining varying quantities of fluorine material with constantquantities of the other ingredients, in a mill addition opacifleraccording to the invention, on the opacity and color of a porcelainenamel opacified therewith; Fig. 2 is a graphic representation of theeffect of time and temperature of calcination on mill additions,according to the invention, as measured by the opacity of the enamelopacifled therewith; Fig. 3 is a graphic representation of thecomparative efiects of varying amounts of tin oxide and a typical milladdition according to the present invention, on two conventional enamelfrits of diverse types as measured by the opacity of the resultingenamel; and, Figs. 4 to 9 inclusive are substantial copies of recordingspectrophotometer charts showing the efiect of various of the novel milladdition opaciflers on the reflectance oi the resulting enamel over therange of the visible spectrum.

We have discovered that certain compositions, the calcination productsof suitable quantities of oxides of antimony (either SbzOs or a loweroxide of antimony together with an oxidizing agent such as nitric acidcapable of oxidizing such lower (ill. Edd-36.2)

oxide to SbzOs) oxide of titanium (TiOz) or oxide of zirconium (Z1 02),or suitable materials capable of yielding one or more of thesame; abasic oxide (such as CaO, BaO, SrO, MgO, A1203, ZnO, or partialsubstitutions of alkali metal oxides therefor), or suitable materialscapable of yielding the same; and a suitable fluorine containingmaterial (such as CaFa, suitably in the form of fluorspar, BaFz, NaF,MgFz, NaaZrFa, CaZrFe, NasAlFs, and materials capable on calcination ofproducing same, such as MgSiFs, HzSiFs plus CaO, MgO plus HF, etc.) whenused as mill addition opacifiers are capable of producing excellentopaciflcation and with no tendency to yellow coloration of the enamel.If, however, the fluorine material is omitted, a distinct deficiency inreflectis slight in the zirconium compositions and more or lesspronounced .in thecase of the titanium compositions.

We believe that complex reactions occur during the calcination but donot completely understand the nature of such reactions. Accordingly, thecalcination products of the ingredients used in the production of thenovel opacifler compositions are treated as containing" certainconstituent oxides and fluorine material, or as having a certaincomposition without thereby intending to limit the invention to anyparticular state of combination, solution or admixture of such oxidesand fluorine material.

We have discovered that upon employment of increasing quantities of thefluorine containing materials, an increasing improvement is noted in thereflectance of violet light up to a point that the objectionable yellowcoloration is no longer perceptible. This bleaching or whitening effectis accompanied by a decrease in opacity (total reflectance of whitelight) up to about the point where the yellow color is no longerperceptible. Surprisingly, however, still further additions of thefluorine containing materials, gradually increase the opacity of theresulting enamel to a value higher than when no fluorine material waspresent. Addition of the fluorine containing material as a smelteraddition in the production of the irit does not produce the desiredeffect. The essential distinction between smelter additions and milladditions, is, as is well known, one of heating time, and, where theterm mill addition or words of like import are used herein, it isintended to cover equivalent procedures where long heating of theupacifler with the frit is avoided. calcination of the ingredients ofthe mill addition opaciflers of the present invention, other than a,

, ance of violet light can be demonstrated, which fled with calciumantimonate alone.-

the fluorine containing material, followed by incorporation of theseparately calcined or uncalcined fluorine-containing material bygrinding, produces a mill addition productive of enamels having theobjectionable yellow coloration to the same extent as it no fluorinecontaining material had been added but with slightly lower opacity.Calcination of calcium antimonate with fluorspar or synthetic CaFa,produces a mill addition pro-j ductive of enamels of lower opacity thanif opaci- Enamels opacified with calcium titanates are white or slightlycreamy in color. The addition oi! fluorspar makes them distinctly yellowand without improving their already poor opacity.' We are aware thatfluorides are commonly used as smelter additions, but, as stated, theyare not effective for our purpose when so used.

We are able to obtain an enamel of very excellent opacity, but deficientin reflectance of violet light, by using as a mill addition opacifler acalcination product of the following composition: I

. Parts by weight CaO 20 SbzOs--- 48 If to the batch of which the abovecomposition weight of a suitable fluorine material, e. g., flu-. orspar,and the resulting calcination product is employed as a mill additionopacifier, an enamel is produced which is free from the objectionableyellow coloration.

The sample composition given above is typical but may be variedconsiderably without departing from the scope oi the invention. Weprefer to operate, and obtain best results by'operating,

within the following range of composition:

Parts by weight CaO 18 to 22 SbaOa 44 to 46 T10 :32 to 34 0am 5 to 30 InFig. l we have shown the results (which are typical of tests usingcompositions in which the Geo, SbaOa and T10: content was the same andthe CaFa content was varied, as indicated. Approximately 17 parts CaO to48 parts Shoot to 35 parts T102 were used, the CaF: content being variedfrom 3.5 to 14. The vertical line A indicates approximately the point atwhich the yellow coloration disappeared. At 5 per cent the coloration isvery slight.

Our experiments indicate that the fluorine material should have aparticle size of from .100 mesh to 200 mesh for best results althoughthe degree of subdivision is not critical.

As above indicated, the oxides need not be employed as such but may beformed from other materials on calclnation. Some sample batchcompositions are as follows:

Partsbywelsht CaC 64.5 CaFa 20.0 sbloa 35.0 T10: 62.0 HNO; (conc.) 32.0

CaCOa 40.6 Cal 34.6 SbaOa 68.6 T10: 56.6 H2O 24.0 Ca(NO:)a.H-l0 33.4

ZnO 44.8 T102- 66.2 SbaOa 30.0 NaF. 40.0 HNO: (conc.) 28.0

38.003; 394.0 1102' 240.3 811203-"; 291.5 CaFa 105.0 HNO; (conc.) 150.0

NaNOa 42.5 CaCm 150.0 TiO: 240.0 SbaOa 291.0 NaF..- v 80.0 HNO; (conc.);L 115.0 CaCOa t e 100.0 MgCO: 168.6 T10: 240.3 SbzOa 291.5 MgSiFt 80.0HNO; (conc.) 80. 0

MgCOa 253.0 T10: 240.0 SbaOa 291.5 MgSiFc 80.0 HNO: (conc.) 80.0

CaC 59.2 Sta-.0: 86.3 ZrO: 71.0 NaaZrFo 30.0 HNO: (conc.) 40.0

are required at 1000 C. While other-temperatures may be usedsuccessfully, as indicated in Fig. 2, we prefer five hours or longer at1000 C. to o c.

The above described mill-addition opaciiying compositions are suitablefor use in enamel irits generally for production of white enamels. InFig. 3 we have compared our novel mill addition with tin oxide in a lowreflectance enamel (curves I5 and I6), and in a super opaque enamel(curves i1 and i8), using the calcination prodnot of the'batch formulafirst above given. The samples corresponding to the lines i5 and H wereopacified with tin oxide in the quantities shown, while the samplescorresponding to the lines l6 and I! were opacified with acalciumantimony-titanium-fluorlne composition according to theinvention, as indicated.

iii

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The following examples will be illustrative of the effect of typicalexamples or our novel mill additions on the resulting enamels in respectt reflectance of violet light:

Emmple I Composition of mill addition: I

CaO parts by weight" 16.6 SbzOs do 47.7 TiOz do 35.5 Amount ofmilladdition agent added to enamel irit percent 6 The reflectance ofviolet light in this case is shown clearly in Fig. 4, whereinreflectance in per cent ('MgCO3=100%) is plotted against wave length oflight. This view is a substantial copy of a test sheet made on arecording spectrophotometer. In this view, the linei (broken) wasproduced by an enamel opacifled with the above composition; the line 2(full) was produced by an enamel opacified with a composition similarexcept being calcined with parts by weight fiuorspar.

Example II Composition of mill addition:

ZnO -parts by weight 22.3 373205 do 44.5 TiOz do 33.1 Amount of milladdition agent added to enamel frit per cent 6 The reflectance of thisexample is shown in Fig.

5, the line 3 (broken) being a record of a test on an enamel containingthe above opacifier. The line 3 (full) is a record of a test of anenamel opacified with a composition similar to that above except beingcalcined with 20 parts by weight of sodium fluoride.

Example III Gomposition of mill addition:

CaO parts by weight 7.8 A1203 dO 14.2 SbzOs do 44.5 TiO2 do 33.4 Amountof mill addition agent added to enamel frit per cent 6 The reflectanceof this sample is shown in Fig. 6, the llne 5 (broken) being a record ofa test on an enamel containing the above opacifler. The line a (full)shows the result of a test of an enamel opacified with a compositionsimilar to the above'except being calcined with 13% of fiuorspar. Theline i (dot and dash) shows the result of a test on an enamel opacifiedwith a composition like that above except for the substitution ofcryolite for a part (25%) of th fiuorspar. Example IV Composition ofmill addition:

(JaO "parts by weight-- 14.0 813205 ..-d0-...... 40.0 ZrO'a do 46.0Amount of mill addition agent added to enamel frlt per cent 6 In Fig. '7we have shown by the line 8 (broken) the reflectance of a porcelainenamel opacified with the above composition and in line 9 (full) the.same but opacified with a composition varied in that with the abovecomposition was calcined 11.3% oi Nai Example V Composition of milladdition:

Ca0 "parts by weight" 14.0 SbzOs d0 40.0 ZrOz do 46.0 Amount of milladdition agent added to enamel irit "per cent- 6 In Fig. 8 we have shownthe results of reflectance tests in porcelain enamel of the aboveopacifier composition (line it, broken) and a composition similar exceptfor the calcination therewith of 20 parts by weight of N'azZZF's (lineH, full).

Example VI Composition of mill addition:

CaO "parts by weight 23.0 SbcOs do 45.5 T102 do 31.1 Amount of milladdition agent added to enamel frit"; per cent 6 In Fig. 9 we have shownthe results of opacification with the above composition (line l2,broken), with the same as varied by calcining therewith 20 parts byweight of fluorspar (line 13, dot and dash), and also as varied bygrinding with the calcined composition 20 parts by weight of previouslycalcined fiuorspar (line it, full). It will be noted that when thefluorine material is calcined with the other constituents of the milladdition, the desired effect is pro- 08.0 13 to 22 513205 44 to 46 T102;32 to 34- fiaFz 5 to 3. Process of making a vitreous enamel comprisingthe steps of firing together at from about 1000" C. to about 1150 'C.,in an oxidizing atmosphere, materials productive of the following:

Parts by weight CaO 18 to 22 SbcOs 44 to 46 T1012 32 to 34 CaF-z 5 to 30introducing the resulting calcination product into an enamel frit inquantity to develop substantial opacity, and grinding.

4. In making vitreous enamels, calcining to gether at temperaturesbetween about 1000 C.

and about 1150 C. for at least three hours, 02.0, SbiOs, T102 and CaF'z,and introducing the calcination product into an enamel irit as a milladdition opacifier. I 5. A mill addition opacifier for vitreous enamels,the same being a calcination product and containing approximately:

Parts by weight 20 Geo SbiOs 46 Z102- 34 NazZrF'a 14 6. A new milladdition opacifier for vitreous enamels, the samebeing a calcinationproduct of calcium and antimony oxides together with titanium andzirconium oxides and a fluoride, and capable of opacifying a vitreousenamel without imparting thereto a yellowish color effect due to poorreflectance in the light wave length range 400 to 450 millimicrons.

7. A new mill addition opacifler for vitreous enamels, the same being acalcination product containing oxides of calcium, antimony, an elementof the class consisting of titania and zirconia anda fluoride, and beingfree from the characteristic of producing yellow coloration in enamelsopacified therewith to the extent that it is capable of imparting to avitreous 'enamela reflectance higher in the light wave length range 400to 425 millimicrons-than in the range 500 to 700 millimicrons suchenamel being one which if opacified with a mill addition not containingfluorine but otherwise identical in composition, manufacture and use,would exhibit an average reflectance more than five per cent lower inthe violet range from 400 to 425 millimicrons than in the range 500 to700 millimicrons.

8. A new mill addition opacifier for vitreous enamels, the same being acalcination product containing oxides of calcium, antimony, an elementof the class consisting of titaniaand zirconia, and a flouride, andbeing free from the characteristic of producing yellow coloration inenamels opacified therewith to the extent that it is capable ofimparting to a vitreous enamel a reflectance higher in the light wavelength range 400 to 425 millimicrons than'in the range 500 to 700millimicrons, calcium oxide being present to the extent of atleast'approximately 14% of the combined weight of said oxides, titaniaor zirconia being present to a substantially greater extent than calciumoxide, antimony oxide being present to a substantially greater extentthan any other oxide and fluoride being present to the extent of from 5to 30% of' the combined weights of the said oxides.

9. A new opacifier for vitreous enamels, the same being a calcinationproduct containing oxides of calcium, antimony and titanium and alsocontaining a fluoride, calcium oxide being present to the extent of atleast approximately 14% of the combined weight of said oxides, titaniabeing present in greater proportion than calcium. oxide and antimonybeing present in greater proportion than titania, the fluoride beingpresent in proportion from 5% to 30% of the combined weight of saidoxides.

10. A new opacifler for vitreous enamels, the

same being a calcination product containing essentially oxides ofcalcium, antimony and, cancer more oxides of the class consisting oftitania and zirconia together with.a fluoride, calcium oxide eingpresent to the extent of atleast approximately 14% of the weight of saidoxides, the oxide or oxides of the class consisting of titania and ofoxy-compounds of calcium, antimony and titanium, capable of yielding oncalcination approximately: r

- Parts by weight Ca'O 18 to 22 SbzOs 44 to 46 T102 32 to 34 togetherwith a fluoride in proportion from 5% to 30% of the said oxides.

12. A mill addition opacifier for vitreous enamels, the same being theproduct of calcination of oxy-compounds of calcium, antimony andtitanium, capable of yielding on calcination approximately:

Parts by weight CaO 18 to 22 SbaOs 44 to 46 TiOz 32 to 34 together withcalcium fluoride inproportion from 5% to 30% of the said oxides.

13. A mill addition opacifler for vitreous enamels, the same being acalcination product and containing CaO, CaFz, SbaOs and TiOz inapproximately the proportions:

Parts by weight Calcium compounds 23 to '52 Antimony oxide 44 to 46Titania 32 to 34 calcium fluoride being present to the extent of atleast five parts by weight.

14. An opacifier for. vitreous enamels, the same being the product ofcalcining materials capable of yielding upon calcination approximately:

Parts byweight CaO--- g 17 to 22 SbaOs 44 to 48 T102 32 to 35 CaF9 3.5150 30 15. Process of making a. vitreous enamel comprising the steps offiring together at from about 1000 C. to about 1150 C., in an oxidizingatmosphere, materials productive of the following:

Parts by weight CaO 17 to 22" SbzOs 44 to 48 T10: 32 to 35 Cal: 3.5 toso introducing the resulting calcination product into an enamel frit inquantity to develop substantial opacity, andgrinding.

J. HARSHAW. WILLIAM D. smmwmn

